Liquid crystal displays driving with a relatively few amount of power are widely adopted to stationary devices as well as portable devices. In such liquid crystal displays, the characteristics concerning display quality, such as a response speed, vary as a temperature of a liquid crystal panel varies. To solve this problem, Patent Document 1 (Japanese Laid-Open Patent Application No. 5-173153/1993 (Tokukaihei 5-173153; published on Jul. 13, 1993)) discloses a liquid crystal display which is provided with a heater for causing the whole display panel to have a uniform temperature, in order to restrain the degradation of display quality.
Meanwhile, liquid crystal displays in general have a slower response speed than CRTs (Cathode-Ray Tubes) and other display devices. A response sometimes is not completed, because of a grayscale level transition, within a rewriting period of time (16.7 msec) that corresponds to an ordinary frame frequency (60 Hz). In view of the circumstances, a method is adopted in which a driving signal is modulated and driven so as to facilitate a transition from a previous current grayscale level to a current grayscale level, thereby improving the response speed. Note that a liquid crystal display adopting such a method is disclosed in FIG. 4 of Patent Document 2 (Japanese Patent No. 2650479; registered on Sep. 3, 1997).
For instance, in the case where a grayscale level transition from a previous frame FR(k−1) to a current frame FR(k) is carried out based on “rise” drive, a voltage is supplied to a pixel so as to facilitate the transition from a current grayscale level to a current grayscale level. More specifically, a voltage having a higher level than a voltage level indicative of an image data D(I, j, k) of the current frame FR(k) is supplied to a pixel.
As a result, when a grayscale level transition occurs, a brightness level of a pixel changes more rapidly, and reaches, in a shorter period of time, near a brightness level that corresponds to image data D(I, j, k) of the current frame FR(k), as compared to a brightness level in a case where a voltage level indicative of image data D(I, j, k) of the current frame FR(k) is supplied from the beginning. This ensures to improve the response speed of the liquid crystal display even when the response speed of the liquid crystal is slow.
However, as in Patent Document 2, such a liquid crystal display facilitating the grayscale level transition facilitates the grayscale level transition from the previous frame to the current frame by correcting image data regarding the current grayscale level of the pixel, so that the pixel receives corrected image data rather than the current image data. Thus, unless the grayscale level transition is appropriately facilitated, excess brightness due to overfacilitated grayscale level transition or poor brightness due to insufficiently-facilitated grayscale level transition may occur.
If, to properly facilitate the grayscale level transition irrespective of the change of the ambient temperature, look-up tables (LUTs) corresponding to respective temperatures are provided, the number of the LUTs for circuits facilitating the grayscale level transition is increased, causing the circuit arrangement to be complicated.
Meanwhile, when a heater is adopted as in Patent Document 1, circuits for, e.g. estimating a temperature and controlling heating by stages have to be provided in order to highly precisely control a temperature (e.g. in a range of about ±1° C.), and this complicates the heater and a temperature control circuit for controlling the heater. Furthermore, even with these estimation circuit and control circuit, when the ambient temperature changes more than anticipated, the temperature control circuit increases a quantity of heat to be significantly larger than a usual quantity, in order to cancel out the change of the ambient temperature. In this case, the attempt to precisely control the temperature by the estimation circuit and control circuit could result in an unnecessarily high temperature of the liquid crystal panel, due to, for instance, mis-estimation.
In a structure of facilitating the grayscale level transition as in Patent Document 2, corrected image data rather than current image data is applied to a pixel. On this account, when a temperature of the liquid crystal panel is unnecessarily high, the grayscale level transition is overfacilitated so that the excess brightness occurs, and this causes significant degradation of display quality.
In light of this problem, the inventors of the present invention have found that a liquid crystal display facilitating a grayscale level transition is different from typical liquid crystal displays, to the extent that highly-precise control of a temperature does not always result in the prevention of the degradation of display quality. The objective of the present invention is thus to provide a liquid crystal display which realizes, with a simple circuit arrangement, an improved response speed while restraining the degradation of display quality on the occasion of the change of the ambient temperature to be hardly recognizable for the viewer.